1. Field of the Invention
The present invention relates to a manufacturing method of a bearing member used in a fluid dynamic bearing of a motor, and to a manufacturing method of a sleeve unit.
2. Description of the Related Art
Conventionally, a recording disk drive device such as a hard disk drive includes a spindle motor (hereinafter, referred to as a “motor”) for driving a recording disk. In recent years, there has been great demand for a motor including a bearing mechanism which utilizes a dynamic pressure. Such a bearing mechanism has a configuration in which a thrust bearing portion or a radial bearing portion utilizing a dynamic pressure of lubricating oil which is provided in a space between a shaft (and a portion connected thereto) and a sleeve or the like.
For example, a technology related to a thrust bearing portion having a configuration in which an annular shaped flange portion is provided at a top side of a sleeve housing surrounding the sleeve, and a top surface of the flange portion having formed thereon a plurality of dynamic pressure grooves and a bottom side of a rotor hub are opposed to one another has been disclosed. Also, a technology in which a bottom surface of the flange portion and a discoid member which is attached to the rotor hub are opposed to one another, whereby preventing the rotor hub from being pressured upward in an excessive manner while the motor is in motion, has been disclosed.
Also, a technology in which the annular shaped flange portion which is arranged between, in an axial direction, the bottom surface of the rotor hub and the top surface of the discoid member is provided at the top of the sleeve or the sleeve housing, wherein the sleeve housing is formed by press working, has been disclosed.
While the motor as described above is in motion, due to a floatation of the rotor hub, a minute gap will be generated between the top surface of the flange portion and the bottom surface of the rotor hub, and between the bottom surface of the flange portion and the top surface of the discoid member. Because the gaps are influential factors on the characteristics of the motor, the gaps are precisely designed, and therefore, a dimensional tolerance of an axial thickness of the flange portion used therein is extremely small.
Also, when the sleeve housing including the flange portion as described above is formed by press working, due to an abrasion of a die used therein, it becomes difficult to maintain a predetermined thickness for the flange portion in a continuous manner. Also, burrs formed at an edge of the flange portion during press working may have a negative impact on the characteristics of the motor. Also, there is a possibility that particles of metal powder of the flange portion after press working or those of a die assembly used during the process may be attached to the bottom surface of the flange portion, thereby contaminating the lubricating oil.